Automatic control system for rotating wing aircraft



12 Sheets-Sheet 1 0 WW Z 3 w W 3 4 3 ./O i \w avlmll @ivilwlil INVENTOR.

H. T. AVERY AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 FlE L Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet 2 INVENTOR WZW H. T. AVERY Jan. 17, 1956 AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT l2 Sheets-Sheet 3 Original Filed May 15, 1946 INVENTOR.

Jan. 17, 1956 H. T. AVERY 3 AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet 4 [N V EN TOR.

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Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet 5 FIE-E 2230 223 L 2303 23/17 222 225 I 0 .230a I R 223 203 o O 204' 222 R L 207 234 B INVENTOR MHZ/4w Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15. 1946 12 Sheets-Sheet a f/fl' 20/ 205" R Z39, W; C90 202? 3% 0 fwd o 2652: 7&46

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R Z; a v 6 Z576 L v L 04a 5 g /04 Z30 INVENTOR .MIZW

Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet '7 INVEN TOR Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet 8 FJLLELLLE J/f 3/7 [III II} N 3/6 3/2 -3/3 330 76 ava 73 FILE- LE.

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WZW

Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet 9 F'QLIEE L& FQLE E I N VEN TOR:

Mai/ W Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet l0 FLE LE INVENTOR:

H. T. AVERY Jan. 17, 1956 AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT l2 Sheets-Sheet 11 Original Filed May 15, 1946 3 v INVENTOR.

Jan. 17, 1956 H. T. AVERY 2,731,215

AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Original Filed May 15, 1946 12 Sheets-Sheet 12 #82 /59 /j 5 0 #l /1 465 M. l 70 INVENTOR United States Patent AUTOMATIC CONTROL SYSTEM FOR ROTATING WING AIRCRAFT Harold T. Avery, Oakland, Calif., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware 33 claims. or. 244-4113 The present invention relates to helicopters, and particularly to the controls which serve to keep the operation of the craft in accord with the performance desired by the operator of the craft.

Up to the present time all aircraft have required a relatively high degree of training and/ or skill to operate. With the airplane this has been primarily due to the relatively high craft speed required to maintain control of the craft. The helicopter entirely gets away from this necessity of thus maintaining airspeed, and therefore would be one of the easiest of all vehicles to operate were it not for the fact that as so far known and operated the helicopter has peculiar operational difficulties of its own. These difficulties are primarily traceable to the fact that the helicopter is capable of a greater variety of kinds of movement than the airplane, and it has been customary to provide separate manual control for each of these various kinds of movements in the helicopter to an extent which increases the number of various control devices with which the operator must continuously be concerned distinctly above that customary. in the airplane. Combined with the extent to which these various movements and control functions are inextricably inter-related in the helicopter, this has rendered the controlling of a helicopter equipped with conventional controls as known in the art, more difficult than the controlling of the airplane in spite of the fact that the most serious airplane control dir'ficulties are eliminated. I

For instance, if it is desired to increase forward'speed on a typical prior art helicopter it is ordinarily necessary for the operator to (l) readjust a pitch control lever to increase the pitch of the rotor blades, (2) readjust the setting of the engine throttle to secure proper engine and rotor speeds, (3) readjust steering pedals to accurately counteract the rotor torque which has thus been increased, (4) readjust the lateral position of the control stick first to balance the increase in counter-torque, and then as the speed of the craft increases to compensate for the greater difierential between the lift exerted by the advancing and the receding blades, and (5) rock the control stick forward to increase forward tilt of the craft so as to convert the additional power into forward movement rather than upward movement, and return the stick to its normal position again when the tiltof the craft has been sufficiently increased. If all five of these controls are not readjusted in exactly the right amounts and the right synchronism and/or sequence the craft will commence to perform one or more unwanted movements or gyrations. Obviously this number of control movements is not too easy to properly co-ordinate without a high degree of skill and training. This is particularly unfortunate in view of the fact that the helicopter seems to otherwise have very promising potentialities for becoming the widely used personal craft of the air.

It is an object of this invention to simplify the con- "ice . 2- trol arrangements for helicopters and to render it easier to properly manipulate them.

It is also an object to provide such a grouping and arrangement of the various manual control members as will not only result in an unprecedented degree of convenience in controlling the craft, but will be so simple and logical in arrangement as to render the operators control of the craft inherently correct with little or no training required.

.It is an object of the invention to automatically substantially prevent sideward movement of a helicopter relative to the air during forward flight except in measured response to the operators setting of a lateral control member, which however, is so arranged that the operator does not need to position it in normal flight.

Itis 'a' further object of the invention to automatically resist displacement of the craft by gusts, particularly under hovering conditions.

It is also an object to render it particularly easy for the operator to hold the craft stationary relative to the ground under all air conditions.

It is an object of the inventionto provide automatic lateral control of the craft with means for automatically altering that control to better adapt it to different flight conditions, and particularly to changes in the longitudinal movement of the craft.

It is also an object to provide means selectively avail-- able to the operator for automatically steadying the craft relative to the ground, or relative to the surrounding air, or both.

It is an object to provide a means for automatically resisting accelerations of the craft from any source including changes in the velocity of the sustaining air relative to the ground, and other means for automatically controlling movement of the craft relative to the air.

it isa further object to provide a unitary manual means for selectively bringing either one or both of these means into operation, and it is alternatively an object to auto matically bring one or the other into operation in response to changes in the flight condition of the craft. This may, for instance, take the form in which the forward speed of the craft automatically determines whether the lateral control mechanisms will act to automatically resist lateral accelerations of the craft or to automatically eliminate lateral movement of the craft relative to the air.

It is a further object to automatically compensate for tilting of the craft fuselage from such sources as eccentric loading. lvlore specifically it is an object to control rotor tilting with respect to the true vertical rather than with respect to the fuselage ofthe craft.

It is an object to automatically control the craft to move laterally at a preselected speed.

It is a further object to automatically bank a helicopter properly for each turn.

It is an object of the invention to automatically maintain forward flight at preselected speeds.

It is a further object to readjust under a unitary control both the automatic lateral controls and the automatic longitudinal controls from conditions controlling for one flight condition to those controlling for another, for instance from controlling for hovering to controlling for cruising.

It is a still further object to provide means for automatically maintaining flight at any preselected speed, in conjunction with a normal manual control member the displacement of which forward or backward from neutral will always cause corresponding forward or backward increments of controlling effect, respectively, including the increase or decrease of craft speed from the preselected speed. That is, it is an object to maintain the normal functioning of the regular manual longitudinal 3 control means in spite of the setting of the automatic longitudinal control means to a preselected speed, which speed will be automatically maintained if the manual. means is not displaced from neutral but will be altered selectively by any such displacement.

It is an object of the invention to so improve the arrangement of lateral controls that the response of the craft thereto will be substantially instantaneous and more perfectly uniform in amount than has heretofore been attainable with articulated sustaining rotors.

It is an object to provide improved means for readjusting the controls for different locations of the center of gravity of the craft, and to thereby avoid the necessity for the operator to hold any of the normal flight control members in a displaced position to correct for such shifts in the center of gravity.

It is an object of the invention to provide a helicopter which can be safely flown for limited but reasonably extensive periods of time with hands off of all controls, and it is a further object to provide such a craft with a maximum of simplicity and at a minimum of cost.

It is an object to render control'of the craft especially easy under cruising conditions, and more specifically it is an object to do this by minimizing the number of control members that need be operated under cruising conditions and the frequency with which any such members need be operated. It is a further object to accomplish this without looking or disabling any of the normal manual control members.

The manner in which the foregoing, together with additional objects and advantages of the invention, are attained will be made apparent in the course of the following description of the preferred embodiments thereof which is to be read with reference to the accompanying drawings, in which:

Figure 1 is a schematic view in perspective showing a portion of the rotor of a craft embodying my invention, particularly the rotor hub and driving shaft, a portion of a typical blade and the means for controlling the pitch of the blades, several of the parts being partially broken away in order to better expose other parts to view.

Figure 2 is a drawing showing schematically the novel means for transmitting the cyclic pitch control movements to the rotor.

Figure 3 is a side elevation of the form of helicopter in which I prefer to incorporate my invention.

Figure 4 is a horizontal section of the same craft taken substantially on line 4-4 of Figure 3.

Figure 5 shows a portion of the louver mechanism illustrated in Figure 4, but on a larger scale and with the louvers occupying a setting difierent from that illustrated in Figure 4.

Figure 6 is a drawing showing schematically the principal automatic controlling mechanisms of the craft, the principal manually movable members for exercising con trol of the craft, and the general nature of the relationship of these to eachother.

Figure 7 is a side view of a control column carrying control members arranged as schematically indicated in Figure 6.

Figure 8 illustrates schematically a mechanism intended to be operated by the automatic steering control mechanism of Figure 6 to control the amount of torque set up by each of the two counter-torque mechanisms with which the craft is preferably equipped.

Figure 9 is a schematic showing of a second embodiment of the mechanism for automatically exercising lateral control of the craft.

Figure 10 schematically illustrates a third embodiment of the lateral control mechanism.

Figure 11 schematically illustrates a second embodiment of the longitudinal control mechanism.

Figure 12 is a schematic view of the mechanism for automatically adjusting the vertical tail fin, which fin is shown as sectioned substantially on the line 1212 of Figure 3.

Figure 13 is an enlarged detailed view of a portion of the mechanism illustrated in Figure 12.

Figure 14 is an elevation (looking forward) of the preferred embodiment of the primary means through which the operator controls the craft.

Figure 15 is a right side view of the same mechanism with the control column cut in section to expose certain of the mechanism within it.

Figure 16 is a view corresponding to the upper art of Figure 15, but on a larger scale and showing additional mechanism not included in Figure 15, and also showing the pitch control lever in section instead of complete, as in Figure 15.

Figure 17 is a section taken substantially on line 17--17 of Figure 16.

Figure 18 is a view corresponding to the lower part of Figure 14, but with the control column and most of the mechanism sectioned in the mid-plane of the column.

Figure 19 is a perspective view showing the emergency means operable by the operator to convert any or all of the automatic control functions to direct manual control.

Figure 20 is a perspective view of the mechanism operated by a typical one of these emergency means, and showing additional details of the manual and automatic control mechanisms.

A. Rotor construction (Fig. 1)

Figure 1 illustrates schematically a typical rotor such as may be used for sustaining a craft embodying my invention, which rotor is in turn controlled by certain of the novel mechanisms of my invention.

The arrangement shown in Figure 1 for transmitting the drive and pitch control movements to the rotor blades corresponds in general to that of the NX-1272 helicopter illustrated and described in an article in Aviation for June 1945 at pages 122 to 130, to which article reference may be had for details of construction previously known in the art and therefore not disclosed herein. A rotor drive tube 10 is adapted to be driven in a counterclockwise direction by an engine mounted in the fuselage of the craft. integrally attached to the upper end of the shaft 10 is a hub member 11 which, in the particular form illustrated, has three arms 12 to each of which ablade such as the blade 17 is pivotally attached by a substantially horizontal hinge 13, only one of the three hinges and blades being shown in the drawings, however. Each blade 17 includes a blade root member 14 which is pivotally attached to the hub member 11 by one of the hinges 13 and is pivotally connected to a blade spar 15 by a pivotal mounting 16, which permits each spar 15 to be rocked on its own axis relative to the root member 14 to change the pitch of the blade. The blade shell 17a is integrally attached to spar 15 by means of ribs 18. This constitutes what is generally termed an articulated rotor. Optionally each blade may also be equipped with a generally vertical drag hinge (now shown) and/ or other cushioning means between the engine and the blades, but the presence of any or all of such hinges and meansdoes not appreciably alter the functioning of the novel mechanism of the craft.

Control means are provided which, by selective adjustment, may cause either simultaneous and equal change of pitch of all blades or may cause the pitch of each blade to be cyclically increased and decreased'as the rotor rotates, the angular location and magnitude of such cyclic changes being dependent upon the direction and magnitude of movement, respectively, of elements of the control means. i

This control means comprises a pitch control arm 20 integral with each blade 17 and pivotally connected for universal movement to the upper end of a pitch control link 21. The lower end of each link 21 is pivotally connected for universal movement to one of three arms 22 of a pitch control spider 23. Integral with spider 23 are cross members 24 which extend inwardly through slots 25 in the rotor drive tube and are pivotally supported by a ball 26 on the upper end of a pitch control rod 27; this arrangement being such that spider 23 is constrained to rotate with shaft 10. Through a thrust bearing mounting of the general character disclosed in the article previously referred to, spider 23 is connected to a non-rotating ring 28; the arrangement being such that spider 23 and ring 28 may be tipped as a unit in any direction by control movements imparted to ring 28. Integral with the ring 28 at two positions, preferably 90 removed from each other, are two arms 30 and 31 which are universally connected to two control rods 32 and 33, respectively, which control rods are subject to displacement in a substantially vertical direction in a manner to be hereinafter described. Vertical movement of control rods 32 and 33 may thus be utilized to effect tilting of ring 28 in any desired direction.

Spider 23 and ring 28 also may be raised or lowered as a whole, without altering their tilt, by raising or lowere ing the pitch control rod 27 upon which they are uni versally mounted by means of the ball 26, and means to be hereinafter described, are provided for vertically positioning rod 27. Such raising or lowering will correspondingly increase or decrease the pitch of all blades; the movement of the pitch control rod 27 introducing a simultaneous and substantially identical change of pitch to all blades; and links 32 and 33 being constrained to move up and down in unison with rod 27 by mechanism which will be described presently.

Any vertical movement of either or both of the control rod 32 and 33 relative to the pitch control rod 27 will, however, cause a change in the tilt of spider 23 and ring 28 and hence a change in the cyclic pattern of pitch distribution, for if the spider and ring are not perpendicular to shaft 10, they will cause the pitch of each blade to be cyclically increased and decreasedas the rotor rotates, the angular location of these cyclic changes depending upon the direction of tilt of the spider and ring and the amount of the cyclic changes depending upon the amount of tilt of the spider and ring.

These cyclic changes of pitch of the blades tend to bring about a tilt in the eifective plane of rotation of the rotor (without tilting the rotor hub), but the direction of such rotor tilt is, in general, not the same as the direction of spider tilt due to the angle subtended in the plane of rotation between the positions thereon of each arm 22 and its corresponding blade spar and to such elfects as that of blade inertia in displacing the rotational position of the blade at the instant of maximum response from its position at the instant of effecting the adjustment causing the response. Nevertheless there is a definite relationship between the direction of tilt of the spider 23 and ring 28 and the direction of tilt that the effective plane of rotationof the rotor eventually tends to assume as a result thereof.

Control rods 32 and 33 are constrained to move vertically in synchronism with the pitch control rod 27 whenever a general increase or decrease of pitch is to be effected by the latter without changing the tilt of the pitch control spider 23; the arrangement being such as will nevertheless permit independent movement of the control rods 32 and 33 with respect to the pitch control rod 27 for the purpose of changing the tilt of the pitch control spider 23. To provide for this, rod 32 is connected to a tilt-control rod 36, as well as to rod 27, in such a manner that the vertical displacements of rod 32 will be equal to those of rod 27, plus displacements equal or proportional to those of the tilt controlrod 36. Rod 33 is similarly connected to rod 27-and a second tilt control rod 37. Hence each vertical position of rod 36 relative to the craft causes rod 32 to assume a corresponding vertical position relative to the pitch control rod 27 and hence to introduce to ring 28 and spider 23 a certain component of tilt which is maintained unchanged as long as tilt control rod 36 is held stationary, regardless of the vertical movement that may be imparted to the ring and spider by pitch control rod 27 or the change in tilt about the coordinate axis that may be imparted to the rings by the second tilt control rod 37. The second tilt control rod 37, in turn, is connected to the ring and spider in a similar manner to give a similar result with respect to its own axis of tilt.

The mechanism for connecting rod 32 to rods 36 and 27 so that it will respond in the manner above described includes a sleeve 38 slidably mountedon tube 10, but restrained from rotating therewith. In order to constrain sleeve 38 to move vertically in unison with rod 27,

it is pivotally connected to a ring 39 by two coaxial pivot pins 4% (only one of these pins being visible in the draw ing). At a point removed from pins 40, an arm 41 integral with the ring 39 is pivotally connected to the rod 32. Another rod 42 directly on the opposite side of tube it from rod 32, is similarly connected to rings 28 and 39. Although ring 39 will not in general be maintained parallel to ring 28, the diameter of ring 39 which is pivotally connected to rods 32 and 42 will be maintained parallel to and a fixed vertical distance from the diameter of ring 28 to which these links are pivotally attached and hence at a constant average height relative to rod 27, hence constraining the axis of pins 40, which intersects this diameter at its mid-point, to intersect the axis of rod 2'7 at a fixed point in the rod. Hence as rod 27 is moved up or down sleeve 38 moves, correspondingly in unchanging vertical relationship to rod 27, even though separated from it by the walls of the rotating tube 10. Pivotally attached to the sleeve 38 by brackets 44 and 45, respectively, are levers 46 and 47, the outer ends of which are pivotally attached to the tilt control rods 36 and 37, respectively. The mid-points of these two levers are connected by normally vertical links 48 and 49, respectively, to the mid-points of levers 50 and 51, respectively, the inner ends of which levers are pivotally connected to rods 32 and 32, respectively. The outer end of lever 51 is pivotably mounted at 53 on a pin fixed in the framework of the craft, while the outer end of lever 50 is pivotally connected to a link 50a pivotally mounted at Stlb on a pin fixed in the framework of the craft.

This mechanism is therefore such that if with tilt control rods 36 and 37 held fixed, pitch control rod 27 be raised or lowered, sleeve 38 and the inner ends of levers 46 and 47 will be raised or lowered by an identical amount, which through links 48 and '49 will cause the mid-points or levers 50 and 51 to be raised or lowered by half this amount, which levers rocking about their fixed pivots 52 and 53 will cause rods 32 and 33 to be raised or lowered by the same amount as rod 27. On the other hand, if. withpitch control rod 27 held sta tionary, tilt control rod 36 and 37 is raised or lowered,-

the mid-point of the corresponding lever 50 or 51 will be raised or lowered by half as much, thereby causing the corresponding rod 32 or 33 to be raised or lowered by the same amount as the tilt control rod 36 or 37 which was moved.

In order that pitch control rod 27 may raise or lower spider 23 and ring 28 without tilting them, it is essential that vertical movement of rod 2'7 shall cause identical vertical movement of rods 32 and 33. Also, the movement imparted to these rods by tilt control rods 36 and 37 should be related to, but not necessarily identical with that of the latter rods. Therefore, if for any reason it should prove desirable to have anything other than a 1:1 ratio of movement between the respective rods 36 and 37 and their respectively associated rods 32 and, 33, links 48 and 49 may be attached at points further in'or out than :the mid-points of their respective levers, so long as the rod is attached the same fractionaldistance out 7 on each of the levers to which it is attached so as to maintain a 1 1 ratio of movement between rod 27 and the rods 32 and 33. I

It is apparent that the above described mechanism will function so that regardless of the average pitch of the blades as determined by the position of the pitch control rod 27, there will be a specific vertical position of tilt control rod 36 which will bring the diameter of ring 23 which it controls into a position perpendicular to the aXis of shaft 10, and that displacement of rod 36 in one direction from this position will cause tilt of the ring in one direction, while displacement therefrom in the other direction will cause tilt in the other direction; and that the positioning of tilt control rod 37 similarly controls the tilting of the ring in directions perpendicular thereto.

' This tilting will control the cyclic pitch in any desired manner in view of the fact that these two components of tilt may be combined to give any desired direction and amount of tilt to the ring and that when the ring is held perpendicular to shaft all blades are maintained at uniform pitch settings throughout their rota.- tion, while when the ring is tilted the pitch of each blade is cyclically increased and decreased as it rotates, the cyclic position of each increase and decrease depending upon the direction of tilt and the amount of increase and decrease depending upon the extent of tilt. The entire arrangement may, for instance, be so oriented in the craft that tilt control rod 36 will control the tilting that normally affects forward and'backward movement of the craft and tilt control rod 37 control the tilting which normally affects lateral movement thereof.

B. Mechanism for transmitting cyclic pitch control to the rotor (Fig. 2)

in an articulated rotor however, the imparting of a given tilt to pitch control ring 28 does not immediately produce a corresponding and constant effect on the craft. As more fully set forth in my prior application Serial No. 630,745 filed November 26, 1945, now Patent 2,546,881 dated March 27, 1951, the response will, in general, vary markedly with time, particularly if a marked change of tilt is suddenly imparted to pitch control ring 28, and in such case the initial response will ordinarily be predominantly at right angles to the final and intended response.

This is primarily due to the fact that in an articulated rotor the blades are incapable of transmitting directly to the hub moments set up by vertical forces acting on them, but only as the blades readjust their flapping angles and paths of movement can they exert any tilting moments on the craft. Such readjustment is necessarily somewhat gradual and is rendered more so by the fact that the lift forces on the blades depend upon their angles of attack measured relative to the body of air through which they are moving, which angles are not constant for a given pattern of blade pitch angles but vary with changes in the path of movement of the blades. Furthermore if each pitch control link 21 is attached to its corresponding blade outboard of flapping hinge 13, as illustrated in Figure 1, even the pattern of blade pitch angles changes with changes in the the path of movement of'the blades.

The above mentioned prior application discloses means for avoiding the delay which this normally causes in securing the desired response from the craft, and also avoiding the false response at right angles to the desired response, which false response usually appears immediately upon the imparting of any sudden change of tilt to pitch control ring 28, but gradually dies away. The means disclosed in said prior application for accomplishing this constitutes means for transmitting any sudden movement of the primary control members to 'tilt control ring 28 in an azimuth direction temporarily altered to such an extent that the immediate transient response of therotor to the tilting of ring 28 will be in the desired direction, but in properly timed relation to the dying out of this transient response and the appearance of the normal final response the direction of tilt of control ring 28 will gradually swing around to that normally associated with the displacement of the primary control members. The primary control members referred to may be the linkages leading directly from the control stick of a conventionally arranged helicopter, or automatically positioned members for efiecting the same controls. In the present instance they comprise the longitudinal control link 122 (Fig. 7) and the lateral control rack 200 (Fig. 6). d

I have discovered, however, that the transient response may not always be present in amounts corresponding to the amounts of simultaneous deficiencies in the normal response, and that, if the response to a quickly applied primary control movement is not only to be immediate but is to remain substantially constant in amount for a given position of the primary control member, it may be necessary to arrange the connection from the primary control member to pitch control ring 23 in such a inann'er that any quick movement of the primary control member not only causes control ring 28 to be tilted in a direction temporarily difilcr'ing from the normal final direction of tilt associated with the movement of the primary control member, but in an amount also tempora'rily differing from the normal final amount of such tilt.

Figure 2 schematically illustrates an arrangement generally corresponding to that disclosed in the above mentioned prior application for thus temporarily altering the direction of tilt of pitch control ring 28, so that craft response will be immediately and continuously in substantially the direction corresponding to the originating control movement, and in addition comprises means for temporarily altering the amount of tilt of the ring 28 so that the craft rsponse to a given control movement will be continuously more uniform in amount than would ordinarily be possible with the arrangement previously disclosed in said prior application. lust as with the mechanism disclosed in said prior application any quick movement of a related primary control member will cause a gyrato'ry movement of pitch control ring 2-8 in the course of which the ring tilts first in one direction and then gradually changes its direction of tilt until it stands tilted in the direction normally permanently associated with the direction of movement of the primary control member. Unlike the arrangement previously disclosed the amount of tilt or ring 23 will be automatically altered throughout this gyr'atory movement in a manner designed to produce substantial uniformity in the resulting craft response.

Figure 2 schematically illustrates mechanism which it is proposed to interpose between the primary control members and the rotor to cause the pitch control mechanism of the rotor to respond in the manner above described. Movement is transmitted to the mechanism illustrated in Figure 2 by means of links 122a and Ztlila. Link 122a (Fig. 2) is connected by linkage, not shown, to link 122 (Fig. '7) to move in unison with it. Therefore when control colnmn 12% is rocked forward on its pivot 121 (to the right in .Figu're 7) to cause a forward moment to be exerted on the craft it operates through link 122 to move link 122a upwardly in Figure 2 as indicated by the arrow labeled F. Similarly when column is rocked rearwardly to cause a backward moment to be exerted on the craft it moves link 122a downwardly in Figure 2 as indicated by the arrow labeled B. Link 206a of Figure 2 is connected by linkage not shown to rack 200 of Figure 6, which as hereinafter described is automatically reciprocated to control the craft laterally. As hereinafter described rack 2% is displaced downwardly in Figure 6 to produce a leftward moment on the craft, which through the connecting linkage mentioned causes upward movement of link 200a (Fig. 2) as indicated by the arrow labeled L, while for a rightward moment these movements are the opposite and link 200a is-displaced downwardly in Figure 2 as indicated by'the arrow labeled R.

The movements thus transmitted to the mechanism illustrated in Figure 2 by links 122a and 200a is transmitted to tilt control rods 36 and 37 which are shown in Figure 2 and also in Figure 1 wherein is shown the previously described mechanism through which they act to cyclically adjust the pitch of the rotor blades, rod 36 being moved upwardly in both Figures 1 and 2 for tilting pitch control ring 28 in the direction normally associated with a forward moment on the craft and downwardly for a backward moment, while rod 37 is moved upwardly in both figures for tilting pitch control ring 28 in the direction normally associated with a leftward moment on the craft and downwardly for a rightward. moment. It is the conventional practice in helicopters to provide a construction Which is the equivalent of connecting link 122a directly to rod 36 and link 280a directly to rod 37, but in order to eliminate or minimize the effects of the abnormal transient response of the rotor to sudden movements of the primary control members and to overcome the adverse effects due to the slowness in its normal response thereto, I prefer to connect both of the links 122:: and 200a to both the rods 36 and 37 by means of the novel mechanism illustrated in Figure 2.

As illustrated in Figure 2 the longitudinal control link 122a is pivotally connected by stud 77a to lever 77, which is pivotally mounted on the frame of the machine at 77b and carries a stud 77c by means of which it is pivotally connected to piston rod 78, which in turn is integral with a piston 79 reciprocable in a hydraulic cylinder 80. Stud 77c and piston 79 will therefore be displaced vertically in Figure 2 in proportion to the displacement of link 122a. As more fully described in the above mentioned prior application, leakage of hydraulic fluid from one side of the piston to the other is permitted through by-pass 81, the flow through which is controlled by a piston 82 reciprocable in a cylinder 83 and spring pressed outwardly by a spring 84 but integral with a plunger 82a by means of which it may be pressed inwardly to alter the rate of flow. The by-pass 81 and flow control cylinder 83 are integrally mounted on the hydraulic cylinder 80 which is movable in the manner hereinafter indicated.

Integral with cylinder 80 is a plate 85 which includes a slot 85a embracing a stud 86 fixed in the frame of the craft. Pivotally mounted on the stud 86 is a link 87 provided with a slot 87a designed to guide over a stud 88 integrally mounted in the plate 85. The plate 85 and link 87 are provided with identical H-shaped openings 89 which normally stand in registration with each other and a spring 90 is mounted in the openings in such a manner that the upper end of the spring rests against the upper end of both openings and the lower end rests against the lower end of both openings. This causes plate 85 and link 87 to form a two-way yieldable link, which may be either extended .or compressed from its normal length, but either such action will cause compression of spring 90, and the spring will tend to restore the link to its normal length with both of the openings 89 aligned with each other. The mechanism comprising cylinder 80 and its related mechanism, plate 85 and link 87 and their related mechanisms, all as above described and including also parts 115 and 117 to be hereinafter described, will for convenience be referred to as a connecting and regulating unit, and the unit just described will be generally designated by the numeral 91.

A second connecting and regulating unit, generally designated by the numeral 92, is constructed exactly like the unit 91, just described, but is connected up in just the reverse manner, in that it is pivotally mounted on, and receives movement from stud 77c at the point in that unit which corresponds to the point at which unit 91 is attached to the fixed stud 86, namely, at the lower end of link 87' which corresponds to link 87 of unit 91, and unit 92 is attached to the fixed stud 93 at the point which corresponds to that at which unit 91 is attached to and receives movement from stud 77c, namely at the upper end of piston rod 78' which corresponds to piston rod 78 of unit 91. Unit 91 is capable of transmitting movement to lever 94, the left end of which lever is provided with a slot embracing stud 88 of that unit. Similarly unit 92 is capable of transmitting movement to lever 95, the left end of which is provided with a slot embracing stud 88 of that unit.

Lateral control link 200a is pivotally connected at 96a to a lever 96 pivotally mounted on the stud 96b fixed in the frame of the craft and integrally carrying a stud 960. This stud 96c is connected to the connecting and regulating unit 97 in a manner corresponding exactly to that in which stud 770 is connected to unit 91, and stud 96c is further connected to unit 98 in a manner corresponding exactly to that in which stud 770 is connected to unit 92. Furthermore units 97 and 98 are constructed exactly like units 91 and 92 and are pivotally attached to fixed studs 99 and 190 corresponding to studs 86 and 93, respectively, of units 91 and 92.

Unit 98 is capable of transmitting movement to lever 94, the right end of which is provided with a slot embracing stud 101 of said unit (corresponding to stud 88 of unit 92). Lever 94 is, in turn, pivotally connected at a point 182 to link 103 which is pivotally attached at 104a to the left end of lever 184. At its right end lever 104 is pivotally attached at 18412 to link 87 which is the link of unit 98 which corresponds to the previously described link 87 in unit 91. Lever 104 is also pivotally attached at lime to tilt control rod 37.

Unit 97 is capable of transmitting movement to lever 95 through reversing lever 186 and link 1187. To provide for this, the right end of lever 95 is pivotally connected at 198 to link 187, which in turn is pivotally connected at 106a, to lever 106, which lever is pivotally mounted on fixed stud 16612 and is provided at its right end with a fork embracing stud 101 (corresponding to stud 88 of unit 91). Lever 95 is, in turn, pivotally connected at point 109 to link 110' which is pivotally attached at 111a to the right end of lever 111. At its left end lever 111 is pivotally attached at 1111b to link 87', which is the link ofunit 92 which corresponds to link 87 of unit 91. Lever 111 is also pivotally attached at 1110 to tilt control rod 36. The reasons why all of these connections are made in the manner above described will be made clear hereinafter.

The operations which take place in response to displacement of longitudinal control link 122a (Fig. 2)

will now be described. In order to avoid unduly complicating the situation described we shall assume that lateral control link 200a is held stationary while link 122a is displaced. Link 200a will then hold lever 96 stationary and through unit 97 will hold stationary lever 106 and link 107, thus establishing pin 108 as a fixed pivot for lever 95. Also through unit 98 it will hold stud 101 stationary as a fixedpivot for lever 94. With these parts stationary we will now assume that longitudinal control link 122a is displaced upwardly to produce a forward tilt of the rotor. If this displacement is made more slowly than the rate at which piston 79 may be displaced in cylinder as governed by the total flow of hydraulic fluid from one side of piston 79 to the other, then cylinder 80 will remain stationary while piston 79 moves upwardly in unison with link 122a and stud 770. Since under these circumstances plate integral with cylinder 80 remains stationary, and hold stationary the stud 88 integrally mounted in said plate, no movement will be imparted to lever 94.

Since, as we have previously noted, link 200a is serving to hold pin 101 at the right end of lever 94 stationary,

it follows that if the longitudinal control link 200a is not displaced and the lateral control link 122a is displaced more slowly than the rate at which piston 79 can readjust itself in cylinder 80, both ends of lever 9 are held stationary which serves through link 163 to hold stationary pin 104a at the left end of lever 104. However, pin 10411 at the right end of said lever is also held stationary by link 87", which is directly connected to lever 96, which lever is held stationary by link 200a. Therefore, no movement is transmitted to lateral tilt control rod 37 in response to displacement of longitudinal control link 122a at a rate as slow as that assumed.

If the rate of displacement of link 122a is also slower than the rate at which piston 79' may be displaced in cylinder 80 of unit 92 there will be no collapsing of spring 90 in that unit and the movement of stud We will be transmitted directly and unchanged to stud 33' of unit 92, thereby correspondingly raising the left end of lever 95. As we have previously noted link 200:: is serving to hold pin 108 stationary, and therefore lever 95, rocking up about this pin as a pivot raises pin 109 and hence through link 110 raises pin 111a in proportion to the upward movement of link 122a. Pin lllb is at the same time being raised in proportion to the upward movement of link 122a. Lever 111, with both its ends thus being raised in proportion to the upward movement of link 122a, serves to raise longitudinal tilt control rod 36 in proportion to this same movement. Hence when longitudinal control link 122a is moved as slowly as assumed longitudinal tilt control rod 36 is simultaneously displaced in direct proportion and lateral tilt control rod 37 remains stationary.

As previously described, if rod 36 is raised slowly enough its raising will cause simple forward tilting of the rotor, and the rate of hydraulic flow from one side of piston 79 to the other may be such that if link 1221: is moved slowly enough to avoid collapsing of spring 90 it will necessarily be moved slowly enough to eifect simple normal and proportionate tilting of the rotor.

On the other hand, if longitudinal control link 1224: is moved upwardly more rapidly than the hydraulic flow permits pistons 79 and 79 to be displaced in their respective cylinders 80 and 8t), spring 90 of unit 92 will collapse by the amount of the diiference between the movement of stud 77c and that of cylinder 80' relative to piston 79', thus delaying the transmission to rod 36 of a portion of the displacement of stud 770. Also as cylinder 80 and stud 88 are carried upward spring 9%) of unit 91 will collapse by the difference between the displacement of stud 77c and the amount of movement of cylinder 80 relative to piston 79, thus moving lateral tilt control rod '37 upward by an amount proportional to this difference.

For instance, assume that link 122a is given a sudden upward displacement of any given amount. Since cylind'er 8th is incapable of any appreciable sudden displacement relative to piston 79, pin '83 will initially be held substantially stationary. However, a portion of the movement of pin 770 will be immediately transmitted to rod 36 through pin 111]), and lever 11-1, and the balance of the movement which rod 36 normally receives from pin 77c (as in the previously described case of slow displacement) will be thereafter transmitted to rod .36 at'a rate determined by the rate at which cylinder 80' is displaced relative to piston 79 under the stress'exerted by spring 90'. Similarly the hydraulic-cylinder 80 Prevents any appreciable immediate change in the distance fromstud 770 to stud 38, thus resulting in stud '88 being initially moved upwardly substantially in synchronism withstud 77c and rod 37 being raised proportionally. However, spring 90 will return stud 88 to normal and eliminate the displace m'entof rod 37 at a rate dependent upon the rate at which-cylinder '30 canm'ove relative "to piston 79. As previously indicated, any sudden tilt of pitcl1=controlring 28 willprodiice an immediate transient rotor response which will be predominantly at right angles to the final normal response of such a tilt of the control ring but this transient response will gradually die out and the normal response gradually appear. The normal response to an upward movement of rod 37 is a leftward tilt of the rotor but a sudden upward movement of rod 37 will produce a transient response which is predominantly at right angles to the normal response, which transient response will be predominantly forward, in the case of a counter-clockwise rotation of the rotor as herein assumed. If rod 37 is held fixed in the position to which it has thus been displaced the direction of rotor response will gradually swing leftward until it becomes directly leftward, and in general the amount of the rotor tilt may alter as its direction changes.

Therefore the sudden upward movement which, as above described, is imparted to rod 37 by a sudden up ward displacement of link 122a will be predominantly forward, which is the direction of response normally associated with an upward movement of link 122a, but since this is the transient response to the upward movement of rod 37 it appears immediately instead of only gradually over a period of time, as is true of the normal forward response brought about by upward displacement of rod 36. However, instead of holding rod-37 at its maximum displacement until the response becomes leftward, rod 37 is returned to normal as rapidly as the displacement of cylinder 30 relative to piston 79 permits, which rate preferably corresponds approximately to the rate at which the forward response resulting from the displacement of rod 37 disappears and/or that resulting from the displacement of rod 36 appears. This rate preferably varies as a function of the amount of displacement imparted to rod 37 from link 12221, which is proportional to the displacement of plate relative to link 87.

Means are provided for thus controlling the rate of restoration of rod 37 as a function of the displacement of plate 85 relative to link '87-. This means comprises a cam plate pivotally mounted on plate 85-by a pin 25a and including a nose -115b embraced in 'a slot 116 of link 87, so that the plate will be angularly positioned on its pivot in accordance with the displacement of the plate 85 relative to link 87. Plate 115 is provided with a cam slot 115s which embraces a pin 117a integrally mounted in a lever 117-, which in turn is pivotally mounted on plate 85 by means of the pin 117b, andthe upper end of which is arranged to engage the plunger 8 2a and thereby press the piston 82 inwardly to eifect the desired regulation of hydraulic flow.

However, if the above described mechanism is arranged to return rod 37 to its normal position at the rate previously described as desirable, it will not prevent rod 37 imparting some leftward response to the rotor for the immediate transient response to a sudden upward movement of rod 37, while ordinarily predominantly forward will usually also have a leftward .component, and during the time that rod 37 is being returned to normal the rotor response to its displacement is becoming continually more leftward in its directi'on. Therefore if the net over all response to .a sudden upward displacement of link 1 22a is'to remain .inithe truly forward direction as intended something mustbeidoue to introduce a compensating rightward response. l'lThis may be done by imparting the upward displacement to rod 36 at a rate appreciably greater than the :maximum rate which avoids all transient response to .such displacement, for the transient response to a rapidupward movement of rod 36 is toward the right. :Therefore cam plate 115, lever- 117?, and the irelated mechanism controlling th'erate'of displacement 'ofcylinderASO' relative to piston 7-9 are preferably so constructed-as to cause rod 36 to receive 'displaceme'nt from link '2'12'2a just rapidly enough to produce a rightward transient response which will exactly cancel the =leftwarcl"response 13 introduced by the displacement of rod 37. How this structure may be dimensioned to effect this result'is more fully described in said copending application.

As illustrated in Figure 2, lateral control link 200:: is connected to lateral tilt control rod 37 through unit 98 in a manner which exactly corresponds to the manner in which longitudinal control link 122a is connected to longitudinal tilt control rod 36 through unit 92. Also this lateral control link 200a is connected to the longitudinal control rod 36 through unit 97 in a manner which corresponds to that in which longitudinal control link 122a is connected through unit 91 to lateral control rod 37 except for the introduction of reversing lever 106 and connecting link 107. The reversing lever 106 is introduced so that the movement imparted to rod 36 by link 200a will always be for a control direction normally displaced 90 in the direction of rotation (in this case counter-clockwise) from the direction normally associated with the control movement of link 2013a, just as was true of the movement imparted to rod 37 by link 122a. The arrangements are therefore such that rods 36 and 37 are displaced by movements of link 200a in a manner which corresponds exactly to that in which the rods 37 and 36, respectively, are displaced by movements of link 122a.

As previously mentioned, I have discovered that th amount of the immediate transient response to a given control movement may not be the same as the amount of the final normal response to the same movement, in which case the arrangement disclosed in my prior application, above referred to, while securing an immediate and continued response in the desired direction (instead of the prior art response which comprised an immediate response in a wrong direction and a delayed response in the desired direction) will not attain constancy in the amount of the response to any given displacement over any period of time, except in the special case where the amounts of the transient and final responses are equal. Figure 2 shows an arrangement for securing substantial constancy'of response regardless of the ratio'of the transient to the final response. It accomplishes this by so arranging the linkage connecting links 122a and 200a to rods 36 and 37 that the transient displacement imparted to either of these rods by a given displacement of one of the links instead of being equal to the final displacement imparted to the other rod by the same link displacement, will bear thereto the reciprocal of the ratio that thecomponent of the transient response at right angles to the final response bears to the final response. I

For instance lever 94 (Fig. 2) is utilized to displace rod 37 in response to movements of both links 122a and 200a. However, the movement from link 12211 is transmitted to lever 94 through stud 88 at its left end and is related to a transient response, while movement from link 200a is transmitted to lever 94 through stud 101 at its right end and is related to a final response. Therefore if pin 102 is located at a distance from pin 38 which bears to its distance from pin 101 the reciprocal of the ratio that the final response to a given sudden control movement bears to the component of the transient response thereto at right angles to the final response the magnitude of the craft response willbe the same immediately as finally.

For instance, assuming as an illustrative example that the rotor characteristics are such that for any sudden control displacement the component of the transient response at right angles to the final response is half as great as the final response, then if the response of the craft to such control displacement is to remain constant in magnitude the transient displacement imparted to rod 37 by the-sudden displacement of link 1221; must be twice as great as the final displacement imparted to. rod 36 thereby. Assuming, as is true of the arrangement illustrated in Figure 2, that the transient and final displacements imparted to rod 36 by links 200a and 122a are of the same magnitude as the respective transient and final displacements imparted to rod 37 by the respectively corresponding movements of these same links, then the transient response imparted to rod 37 through pin 38 should be twice as great as the final response imparted to it through an equal movement of pin 101, which will be true if, as illustrated, pin 102 is located twice as far from pin 101 as it is from pin 88. Also in order that the same conditions will apply 'to rod 36, which receives its transient movement through pin 108 and its final movement through pin 88, pin 109 should be twice as close to pin 108 as to pin 88', assuming that lever 106 is pivoted at its midpoint so that the vertical movement of pins 106a and 108 will be equal and opposite to that of pin 101.

For a craft in which the rotor characteristics were such that the immediate transient response is exactly at right angles to the final response rod 36 could be mounted directly on pin 109 and rod 37 on pin 102, but as a rule the rotor characteristics are such that the immediate transient response is displaced by less than 90 from the final response in a direction opposite to that of the rotor rotation; Therefore if the immediate response of the craft is to be in the desired direction, the direction in which pitch control ring 28 is immediately tilted must be displaced from its final direction of tilt by this same angle in the direction of rotor rotation. This may be accomplished for a displacement angle of less than 90 by so arranging that any sudden movement of control link 122a will impart. some immediate movement to its final response rod 36 as well as to its transient response rod 37, and similarly link 200a impart some immediate movement to its final response rod 37 as well as to its transient response rod 36. The angle by which the direction of immediate tilt of control ring 28 will depart from the direction of its final tilt will be the angle whose tangent is equal to the movement immediately transmitted to the transient response rod divided by that immediately transmitted to the final response rod. If the ratio of these two movements is made equal to the tangent of the angle by which the direction of the immediate transient response of the rotor characteristically differs from the direction of the final response thereof the immediate response of the craft will be in the desired direction. By locating pin 1040 the proper fractional distance of the way along lever 104 from pin 104a to pin 104b, and pin 111:: the same fraction of the distance along lever 111 from pin 111a to pin 111b this result will be accomplished. This location may be determined as follows:

Let A=the characteristic angle by which the direction of the immediate transient response to a sudden cyclic control movement departs from that of the final re-' sponse in the given rotor.

Let r=the characteristic ratio that the magnitude of the component of said immediate transient response at right angles to said final response bears to the magnitude of said final response. Y

Let d: the amount of a sudden displacement of pin 770.

Let i=the corresponding amount of immediate displacement of rod 36.

Let r=the corresponding amount of immediate transient displacement of rod 37.

Let f= the fractional part of the length of lever 94 lying to the left of pin 102, and also the fractional part of lever 95 lying to the right of pin 109, that is:

f distanoe from 88 to 102 distance from 88 101 distance from 108 to 109 distance from 88 to 108 Let x=the fractional part of the length of lever 104 lying to the left of pin 10 4c, and also the fractional part of the length of lever 111 lying to the right of pin 1110, that is:

distanee from 10401, to 1040 distance from 104a to 10417 distance from 111a to 1110 distance from 111a to lllb It was previously indicated that the distance from 88 to 102 should bear to the distance from 102 to 101 the ratio identified as r above.

As previously indicated, if we are to secure a true direction of immediate response these distances must be so related that which indicates that pin 102 should be one-thirdthe distance from 88 to 101, :and 109 should beone-third the distancefrom 108 to 88.

From Equation 11 l l 51.5 1.7,32+1" E3T5%" which indicates that pin 1040 should be 0.278 of-thedistance from 104a to 104b, and pin .lllcshould lye-0.278 of the distance from 111a to 111b.

Thus Equation 2 enables a designer to proportion a mechanism corresponding to thatschematically illustrated in Figure 2 in a manner insuring a substantially constant magnitude of response a-sudden-control movement, and Equation ll 'enabieshim to proportion it so that that response will be continuously in substantially the desired 'direction,

As previously noted the immediate transient response is usually eifected in a direction which departs by less than from the finalre sponse, that is the angle A is usually less than 90. The above analysis was made on the basis of starting with a determination of the amount of immediate transient response at right angles to the final response. Should it be desired to start instead with the amount of the resultant immediate response effected at angle A to the final response the following additional relationship applies:

Let b=the characteristic ratio that the magnitude of the immediate resultant response bears to the magnitude of the final response.

r=b sin A (12) The following summarizes the movements involved in the Figure 2 mechanism in a somewhat diiferent and simpler manner.

Let D1: the distance through which rod 37 is immediately displaced by a sudden movement of link 122a Let Dz=the distance through which rod 37 is immediately displaced by a corresponding movement of link 200a Let D3=the distance through which rod 37 is later displaced by said movement of link 200a The ratio of D to D1 is determined solely by the proportions of lever 94 and maybe expressed as follows:

The ratio of D1 to D2 depends on the proportions of both levers'94 and 104 and maybe expressed as An exactly similar condition exists for rod 36, by virtue of which Equations 13 and 14 would be equally true, and have a meaning applying to a single original control movement, if with D1 (as before) representing the immediate displacement of rod 37 in response to a sudden movement of link 122a, D2 is assumed to represent the immediate displacement and D3 the later displacement of rod 36 in response to the same movement of link 122a.

C. General arrangement of craft and counter-torque means (Figs. 3, 4 and 5') Figures 3 and 4 illustrate the general form and arrangement of the craft in which my invention is preferably embodied, though it is tobe understood that the invention is by no means limited to use in the type of craft here illustrated, nor in conjunction with the particular rotor arrangement illustrated in Figure 1. As shown in Figures 3 and 4 the engine 60 is connected, through a train comprising appropriate shafts and gearing and including overrunning clutch 61 and hydraulic clutch 62, to the rotor shaft 10 to drive same at a suitable reduction ratio from the engine.

Driven by this train is a rearwardly extending shaft 64 carrying at its rear end the adjustable pitch, axial flow fan 65, which fan is employed for counter-torque purposes. Optionally the clutch64a may be located on shaft 64 for selectively declutching the 'fan from the engine. Control rod 66 may be selectivelypositioned to bring the pitch of the blades of fan 65 to any desired pitch angle throughout a range including substantiallya zero pitch angle at which no air is delivered by the fan, and a'high pitch angle at which the fan willforce a large volume of air rearwardly through the duct .67 in which the fan is located. T he air so delivered maybe drawn in through louvers '68,located on the top and bottom of the'fuse lage and dischargedthrough a'large opening 69 on one side of the fuselage near the tail.

As shown inFigure 4 duct 67 isprovided with turning vanes'70 immediately inside the opening 69, and as also an A ('14:) 

